Photoinduced Skeletal Rearrangement of N-Substituted Colchicine Derivatives.

Colchicine is an active pharmaceutical ingredient widely used for treating gout, pericarditis, and familial Mediterranean fever with high antimitotic activity. The photoisomerization of colchicine deactivates its anti-inflammatory and antimitotic properties. However, despite numerous reports on colchicine derivatives, their photostability has not been investigated in detail. This report reveals the effects of UV-induced rearrangement on the structure and reports the biological activity of new N-substituted colchicine derivatives.

Synthesis and in vitro anticancer activity of new gemcitabine-nucleoside analogue dimers containing methyltriazole or ester-methyltriazole linker.

Two series of novel gemcitabine-nucleoside analogue dimers were synthesized using the 'click' chemistry approach. In the first series of dimers (21-30), the nucleoside units were connected with a stable methyltriazole 4N-3'(or 5')C linker whereas in the second series (31-40) with a cleavable ester-methyltriazole 4N-3'(or 5')C linker. Dimers 21-40 were evaluated for their cytotoxic activity in five human cancer cell lines such as cervical (HeLa), nasopharyngeal (KB), lung (A549), brain (U87), liver (HepG2) and normal dermal fibroblast cell line (HDF) using the sulforhodamine B (SRB) assay. Compound 29 comprising two gemcitabine (dFdC) units exhibited the highest activity among dimers 21-30. The activity of compound 29 was higher than that of dFdC in all the studied cancer cell lines. A similar order of activity was observed for compounds 25, 28, and 30. The best activity among all the dimers synthesized was displayed by compound 39, comprising two gemcitabine units with a cleavable linker. The activity of compound 39 was 5 to 9 times higher than that of dFdC, depending on the cell line. In addition, marked cytotoxic activity was shown by compounds 31, 36, 38, and 40.

Synthesis and anticancer activity of some 5-fluoro-2'-deoxyuridine phosphoramidates.

Two series of novel 4-chlorophenyl N-alkyl phosphoramidates of 3'-O-(t-butoxycarbonyl)-5-fluoro-2'-deoxyuridine (3'-BOC-FdU) (9a-9j) and 5-fluoro-2'-deoxyuridine (FdU) (10a-10j) were synthesized by means of phosphorylation of 3'-BOC-FdU (4) with 4-chlorophenyl phosphoroditriazolide (7), followed by a reaction with the appropriate amine. Phosphoramidates 9a-9j were converted to the corresponding 10a-10j by removal of the 3'-t-butoxycarbonyl protecting group (BOC) under acidic conditions. The synthesized phosphoramidates 9a-9j and 10a-10j were evaluated for their cytotoxic activity in five human cancer cell lines: cervical (HeLa), nasopharyngeal (KB), breast (MCF-7), liver (HepG2), osteosarcoma (143B) and normal human dermal fibroblast cell line (HDF) using the sulforhodamine B (SRB) assay. Two phosphoramidates 9b and 9j with the N-ethyl and N-(methoxy-(S)-alaninyl) substituents, respectively, displayed remarkable activity in all the investigated cancer cells, and the activity was considerably higher than that of the parent nucleoside 4 and FdU. Among phosphoramidates 10a-10j compound 10c with the N-(2,2,2-trifluoroethyl) substituent showed the highest activity. Phosphoramidate 10c was more active than the FdU in all the cancer cell lines tested.

'Click' chemistry synthesis and capillary electrophoresis study of 1,4-linked 1,2,3-triazole AZT-systemin conjugate.

The Cu(I) catalyzed Huisgen 1,3-dipolar azide-alkyne cycloaddition (CuAAC) was applied for a nucleoside-peptide bioconjugation. Systemin (Sys), an 18-aa plant signaling peptide naturally produced in response to wounding or pathogen attack, was chemically synthesized as its N-propynoic acid functionalized analog (Prp-Sys) using the SPPS. Next, CuAAC was applied to conjugate Prp-Sys with 3'-azido-2',3'-dideoxythymidine (AZT), a model cargo molecule. 1,4-Linked 1,2,3-triazole AZT-Sys conjugate was designed to characterize the spreading properties and ability to translocate of cargo molecules of systemin. CuAAC allowed the synthesis of the conjugate in a chemoselective and regioselective manner, with high purity and yield. The presence of Cu(I) ions generated in situ drove the CuAAC reaction to completion within a few minutes without any by-products. Under typical separation conditions of phosphate 'buffer' at low pH and uncoated fused bare-silica capillary, an increasing peak intensity assigned to triazole-linked AZT-Sys conjugate was observed using capillary electrophoresis (CE) during CuAAC. CE analysis showed that systemin peptides are stable in tomato leaf extract for up to a few hours. CE-ESI-MS revealed that the native Sys and its conjugate with AZT are translocated through the tomato stem and can be directly detected in stem exudates. The results show potential application of systemin as a transporter of low molecular weight cargo molecules in tomato plant and of CE method to characterize a behavior of plant peptides and its analogs.

Synthesis of 3'-azido-3'-deoxythymidine (AZT)--Cinchona alkaloid conjugates via click chemistry: Toward novel fluorescent markers and cytostatic agents.

Novel nucleoside-Cinchona alkaloid conjugates were synthesized using 'click' chemistry approach based on the copper(I) catalyzed Huisgen azide-alkyne cycloaddition. Two series of conjugates were prepared employing 3'-azido-3'-deoxythymidine (AZT) as the azide component and the four 10,11-didehydro Cinchona alkaloids as well as their 9-O-propargyl ethers as the alkyne components. All obtained conjugates showed strong fluorescence emission and some of them exhibited marked cytotoxic activity in vitro.

Synthesis and anticancer activity of 5'-chloromethylphosphonates of 3'-azido-3'-deoxythymidine (AZT).

A series of novel N-alkyl 5'-chloromethylphosphonates of 3'-azido-3'-deoxythymidine (6-15) was synthesized by means of phosphonylation of 3'-azido-3'-deoxythymidine (4) with P-chloromethylphosphonic ditriazolide (3) followed by a reaction with the appropriate amine. The synthesized phosphonamidates 6-15 were evaluated for their cytotoxic activity in two human cancer cell lines: oral (KB) and breast (MCF-7) using the sulforhodamine B (SRB) assay. The highest activity in KB human cancer cells was displayed by phosphonamidate 8 (IC(50)=5.8 µg/mL), however, this compound was less potent than the parent AZT (IC(50)=3.1 µg/mL). Phosphonamidate 10 showed only moderate activity (IC(50)=12.1 µg/mL) whereas the other phosphonamidates proved inactive. Similarly, the highest activity in MCF-7 human cancer cells was displayed by phosphonamidate 8 (IC(50)=3.7 µg/mL) but it proved somewhat less active than AZT (IC(50)=2.6 µg/mL). Some activity was also displayed by phosphonamidate 10 (IC(50)=12.8 µg/mL) but the other phosphonamidates were found inactive. Hydrolysis studies indicate that the synthesized phosphonamidates are likely to act as prodrugs of the parent nucleoside (AZT). Transport measurements showed that the most active phosphonamidates (8 and 10) were able to permeate across the intestinal epithelium in vitro. The apparent permeability coefficients determined in Caco-2 cell monolayers indicated that these compounds could be moderately absorbed in humans.

Synthesis and anticancer activity of 3'-[4-fluoroaryl-(1,2,3-triazol-1-yl)]-3'-deoxythymidine analogs and their phosphoramidates.

A series of novel 4-chlorophenyl N-alkyl phosphoramidates of 3'-[4-fluoroaryl-(1,2,3-triazol-1-yl)]-3'-deoxythymidines (20-49) was synthesized by means of phosphorylation of 3'-[4-aryl-(1,2,3-triazol-1-yl)]-3'-deoxythymidines (7-11) with 4-chlorophenyl phosphoroditriazolide (14), followed by a reaction with the appropriate amine. The synthesized compounds 7-11 and 20-49 were evaluated along with four known anticancer compounds for their cytotoxic activity in human cancer cell lines: cervical (HeLa), nasopharyngeal (KB), breast (MCF-7), osteosarcoma (143B) (only selected compounds 20, 24, 28, 32-36, 38, 40, 46) and normal human dermal fibroblast cell line (HDF) using the sulforhodamine B (SRB) assay. Among 3'-[4-aryl-(1,2,3-triazol-1-yl)]-3'-deoxythymidines (7-11) the highest activity in all the investigated cancer cells was displayed by 3'-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3'-deoxythymidine (9) (IC50 in the range of 2.58-3.61 µM) and its activity was higher than that of cytarabine. Among phosphoramidates 20-49 the highest activity was demonstrated by N-n-propyl phosphoramidate of 3'-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3'-deoxythymidine (35) in all the cancer cells (IC50 in the range of 0.97-1.94 µM). Also N-ethyl phosphoramidate of 3'-[4-(3-fluorophenyl)-(1,2,3-triazol-1-yl)]-3'-deoxythymidine (33) exhibited good activity in all the used cell lines (IC50 in the range of 4.79-4.96 µM).

Method of determination of emission properties of very weakly emitting species ensuring elimination of emission of impurities.

This paper describes a new type of spectrofluorimeter, composed of a high-performance liquid chromatography (HPLC) system directly connected to a fluorescence detector and an absorption photodiode array detector, designed for studying the emission of weakly emitting species. Procedures for measurements of emission spectra (ES), emission excitation spectra (EES), and quantum yields of emission (PhiE) for very weakly emitting systems (PhiE>or=10(-7)) have been proposed. The original methodical solution allows verification of whether the emission observed comes solely from the compound studied (and not from its impurities) or from some photochemical or thermal process taking place during measurements. Thanks to the use of this new type of spectrofluorimeter, it is possible to establish with a high probability that the dependence of the shape and position of the ES on the excitation wavelength and the differences between EES and absorptance spectra are due to photophysical and/or photochemical properties of the compound studied and not due to the presence of emitting impurities. An especially interesting application of this method is to study the emission of species whose very weak emission is related to a very short lifetime as well as a low radiative rate constant. It is particularly suitable to the study of the emission properties of flexible molecules that can occur in a few conformers of different absorption and emission properties. The performance of the method is illustrated by the results of the emission studies carried out for Nalpha-acetyl-2-(uracil-5-yl)-L-tryptophan N-ethylamide.

Differences in Antiproliferative Activity Between Salinomycin-AZT Conjugates Obtained via 'Click' and Esterification Reactions.

BACKGROUND: Pharmacophore hybridization by bioconjugation, in which two bioactive moieties are covalently linked, is one of the current strategies in drug discovery for the development of new compounds with improved affinity and efficacy relative to those of the parent molecules. Prompted by the idea that cancer cells may be effectively killed by 3'-azido-3'-deoxythymidine (AZT) and salinomycin (SAL) individually, we synthesized hybrids of these compounds. The development of this type of derivatives, which can easily penetrate the lipid-rich cell membranes and then undergo hydrolysis inside the cancer cells, is an important research area. METHODS: Efficient methods for the synthesis of two new conjugates are presented. The first method is based on the 'click' chemistry and involves the copper(I) catalysed 1,3-dipolar Huisgen cycloaddition reaction. In the second method AZT as well as SAL are connected by the ester bond under mild reaction conditions. The in vitro anti-proliferative activity of both conjugates against several drugsensitive and drug-resistant cancer cell lines as well as toxicity against normal murine embryonic fibroblasts are also determined. RESULTS: Our studies clearly showed that the hybrid obtained via esterification reaction (SAL-OAZT) seems to be attractive in the fight against neoplastic diseases because it helps to overcome a strong drug-resistance of the cancer cell lines examined at low micromolar concentrations. The anticancer activity of this hybrid is also connected with high selectivity indexes (low toxicity) against normal cells.On the other hand, the 'click' conjugate (SAL-AZT) is practically inactive against the drug-resistant cancer cell lines tested and weakly active against the drug-sensitive ones. Also no synergistic effect has been found between SAL and AZT against eight cancer cell lines studied. CONCLUSION: All of our findings support a strategy to decrease the doxorubicin concentration in combination with SAL-O-AZT hybrid in order to reduce the toxicity of this drug, as recently demonstrated for SAL. The advantages of the SAL-O-AZT conjugate over SAL are better RI and SI parameters at similar IC50values.

Synthesis, Antibacterial, and Anticancer Evaluation of Novel Spiramycin-Like Conjugates Containing C(5) Triazole Arm.

Huisgen cycloaddition allowed obtaining of novel triazole-bridged antibiotics (6-16) with the reconstructed C(5) arm of spiramycin. (1)H-(1)H NOESY couplings indicated the structure of novel derivatives in solution and demonstrated that the rebuilt C(5) arm is slightly differently oriented relative to the aglycone part if compared to that of spiramycin (1). Combined analysis of biological data together with experimentally determined lipophilicity (clogP) and solubility show the importance of the chemical nature of the newly introduced triazole C(5) arm in the presence of attractive antibacterial and anticancer potency. The most cytotoxic active triazole conjugates having a hydrophobic and bulky C(5) arm showed higher selectivity toward cancer cell lines (HeLa, KB, MCF-7, Hep-G2, and U87) relative to HDF normal cells than that of the parent spiramycin. Our studies have demonstrated that the aldehyde group is not crucial for the presence of interesting antibacterial [MIC(S. pneumoniae) ∼ 1.2 µM] and anticancer [IC50(HepG2) ∼ 6 µM] properties of 16-membered lactone macrolides based on spiramycin's aglycone.

16-Membered Macrolide Lactone Derivatives Bearing a Triazole-Functionalized Arm at the Aglycone C13 Position as Antibacterial and Anticancer Agents.

A series of new C13-triazole-bridged and C13-ether leucomycin analogues with a reduced aldehyde group were synthesized. Derivatives with the highest antibacterial [MIC values (S. epidermidis, S. pneumoniae): ∼2-4 µg mL(-1) ; 2.55-5.09 µm] and cytotoxic [IC50 values (HeLa, KB, MCF-7, A549, HepG2 cells): ∼1.35-3.70 µm] potencies were those with the best aqueous solubility and bearing a saccharide-triazole arm at the C13 position of the aglycone. These derivatives preferentially bind at the ribosomal tunnel and show the most attractive selectivity indexes [SI; calculated relative to the human dermal fibroblast (HDF) cell line], even higher than that of the reference compound cytarabine. Results of molecular docking studies of this type of macrolide antibiotics at the ribosomal tunnel, together with experimentally determined lipophilicity and aqueous solubility values, as well as biological assay data revealed the importance of the introduced functional group at the aglycone C13 arm to the future design of anticancer and antibacterial drug candidates. Our results clearly indicate that the high antibacterial and anticancer activities of these types of macrolides do not necessarily depend on the presence of the aldehyde group at the aglycone lactone ring.

The photochemistry of thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine in aqueous solution.

The photochemistry of the dinucleoside monophosphate thymidylyl-(3'-5')-5-methyl-2'-deoxycytidine (Tpm5dC) has been studied in aqueous solution using both 254 nm and UV-B radiation. A variety of dinucleotide photoproducts containing 5-methylcytosine (m5C) have been isolated and characterized. These include two cyclobutane dimers (CBD) (the cis-syn [c,s]and trans-syn forms), a (6-4) adduct and its related Dewar isomer, and two isomers of a product in which the m5C moiety was converted into an acrylamidine. Small amounts of thymidylyl-(3'-5')-thymidine (TpT) were also formed, presumably as a secondary photoreaction product. In addition, a photoproduct was characterized in which the m5C moiety was lost, thus generating 3'-thymidylic acid esterified with 2'-deoxyribose at the 5-hydroxyl on the sugar moiety. The c,s CBD of Tpm5dC readily undergoes deamination to form the corresponding CBD of TpT. The kinetics of this deamination process has been studied; the corresponding enthalpy and entropy of activation for the reaction have been evaluated at pH 7.4 as being, respectively, 73.4 kJ/mol and -103.5 J/K mol. Deamination was not observed for the other characterized photoproducts of Tpm5dC.

Synthesis and biological activity of salinomycin conjugates with floxuridine.

As part of our program to develop anticancer agents, we have synthesized new compounds, which are conjugates between well-known anticancer drug, floxuridine and salinomycin which is able to selectivity kill cancer stem cells. The conjugates were obtained in two ways i.e. by copper(I) catalysed click Huisgen cycloaddition reaction performed between 3'-azido-2',3'-dideoxy-5-fluorouridine and salinomycin propargyl amide, and by the ester synthesis starting from salinomycin and floxuridine under mild condition. The compounds obtained were characterized by spectroscopic methods and evaluated for their in vitro cytotoxicity against seven human cancer cell lines as well as antibacterial activity against clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus epidermidis (MRSE). The conjugate obtained by esterification reaction showed a significantly higher antiproliferative activity against the drug-resistant cancer cells and lower toxicity than those of salinomycin and floxuridine towards normal cells, as well as standard anticancer drugs, such as cisplatin and doxorubicin. The conjugate compound revealed also moderate activity against MRSA and MRSE bacterial strains. Very high activity of floxuridine and 5-fluorouracil against MRSA and MRSE has been also observed.

Synthesis of novel 2',3'-didehydro-2',3'-dideoxyinosine phosphoramidate prodrugs and evaluation of their anticancer activity.

An efficient synthesis of 4-chlorophenyl N-alkyl phosphoramidates of 2 ',3 '-didehydro-2 ',3 '-dideoxyinosine employing 4-chlorophenyl phosphoroditetrazolide as a phosphorylating agent is reported. Improved method for the synthesis of 2 ',3 '-didehydro-2 ',3 '-dideoxyinosine starting from inosine is also described. The synthesized phosphoramidates 11-18 were examined for their cytotoxic activity in three human cancer cell lines: cervical (HeLa), oral (KB), and breast (MCF-7) employing sulforhodamine B assay. The highest activity in all investigated cancer cell lines was displayed by phosphoramidate 13 with N-n-propyl substituent.

Phloretamide, an apple phenolic compound, activates the Nrf2/ARE pathway in human hepatocytes.

The aim of this study was to evaluate the effect of phloretamide (PA), an apple constituent, on the activation of the Nrf2 transcription factor and the expression of its target genes: glutathione S-transferases (GSTs), NAD(P)H:quinone oxidoreductase-1 (NQO1) and heme oxygenase-1 (HO-1) in normal human THLE-2 hepatocytes and the hepatoma HepG2 cell line. PA did not show significant cytotoxicity towards THLE-2 cells but such an effect was observed in HepG2 cells (IC(50) ∼200µM). The treatment of cells with PA resulted in the translocation of Nrf2 from cytosol to nucleus in both cell lines, but increased the level of its transcript and protein only in THLE-2 cells. In this cell line an increased level of GSTA, GSTP, GSTT, NQO1 mRNA was also observed. Increased expression of GSTs was confirmed by enhancement of their protein levels. The increase in p53 protein content observed in THLE-2 may be associated with its stabilization induced by the enhancement of NQO1 level. PA did not affect Nrf2, GSTs, NQO1 or HO-1 expression in HepG2 cells. These results suggest that PA has rather chemopreventive than chemiotherapeutic potential and acts similarly as apple dihydrochalcones through the induction of detoxification/antioxidative enzymes.

Synthesis of 3'-azido-2',3'-dideoxy-5-fluorouridine phosphoramidates and evaluation of their anticancer activity.

A series of novel 4-chlorophenyl N-alkyl phosphoramidates of 3'-azido-2',3'-dideoxy-5-fluorouridine (12-21) were synthesized by means of phosphorylation of 3'-azido-2',3'-dideoxy-5-fluorouridine (4) with 4-chlorophenyl phosphoroditriazolide (10) followed by a reaction with the appropriate amine. The synthesized phosphoramidates (12-21) were evaluated for their cytotoxic activity in three human cancer cell lines: cervical (HeLa), oral (KB) and breast (MCF-7) using the sulforhodamine B (SRB) assay. The highest activity in all the investigated cancer cells was displayed by phosphoramidate 13 with the N-ethyl substituent and its activity was much higher than that of the parent nucleoside. Also phosphoramidate 17 with the N-propargyl substituent exhibited good activity in all the used cell lines.